|Publication number||US4389184 A|
|Application number||US 06/224,289|
|Publication date||Jun 21, 1983|
|Filing date||Jan 24, 1980|
|Priority date||Jan 24, 1979|
|Also published as||WO1980001604A1|
|Publication number||06224289, 224289, PCT/1980/8, PCT/JP/1980/000008, PCT/JP/1980/00008, PCT/JP/80/000008, PCT/JP/80/00008, PCT/JP1980/000008, PCT/JP1980/00008, PCT/JP1980000008, PCT/JP198000008, PCT/JP80/000008, PCT/JP80/00008, PCT/JP80000008, PCT/JP8000008, US 4389184 A, US 4389184A, US-A-4389184, US4389184 A, US4389184A|
|Inventors||Toshio Tanaka, Sumio Nakagawa, Kenzi Toudo|
|Original Assignee||Hitachi, Ltd.|
|Export Citation||BiBTeX, EndNote, RefMan|
|Patent Citations (8), Referenced by (10), Classifications (15)|
|External Links: USPTO, USPTO Assignment, Espacenet|
This invention relates to a combustion control apparatus which controls combustion in a combustor which is a heat source of a hot-water boiler or a hot-air heater.
A combustion control apparatus includes a memory circuit which generates an alarm signal and generates also a signal for stopping the combustion in the apparatus and which maintains its non-combustion state, when an abnormal condition such as abnormal heating, shortage of a medium (water) to be heated or ignition failure is sensed.
However, malfunction of such apparatus has occurred frequently due to the fact that this memory circuit is generally easily affected by noise, which can easily enter this memory circuit. This malfunction is objectionable as it may lead to an interruption of the combustion in the apparatus.
In the combustion control apparatus, noise is generated due to on-off operation of electromagnetic relays for various external output units driven by combustion control output signals from a combustion control circuit in the apparatus and also due to on-off operation of a fuel supply unit, a combustion blower and an ignition unit driven by the relays above described. Such noise is applied to the memory circuit through an input circuit and gives rise to a source of malfunction of the apparatus.
It is an object of the present invention to prevent the memory circuit from causing a malfunction by being affected by noise generated from the external output units. More precisely, the present invention comprises a circuit which detects an abnormality signal with timing other than the timing of generation of noise from the external output units, and the output of this circuit is applied as an input to the memory circuit. According to the present invention, malfunction due to noise from the external output units can be prevented in spite of a simple structure.
FIG. 1 is a circuit diagram of an embodiment of the combustion control apparatus of the present invention;
FIG. 2 illustrates operation of various units in the combustion control apparatus; and
FIG. 3 shows operating waveforms at various points in FIG. 1.
The present invention will now be described with reference to an embodiment shown in FIG. 1. In order to simplify the designation of and facilitate the understanding of various input signal terminals and output signal terminals shown in the figure, the word "terminal" may be omitted from them, and they may be designated by suffixing the reference numeral to the name of the signal. For example, "reference clock pulse input terminal 1" may be designated as "reference clock pulse 1". Further, a signal at each of the terminals has a digital value of "0" or "1".
The illustrated embodiment is of a type in which the igniting operation is performed after pre-purging, and the operation of the igniter is stopped when ignition is attained.
Reference numeral 1 designates a reference clock pulse input terminal, and 2 designates a reference timer which is composed of counters 3 and 4. Reference numeral 5 designates a timer for timing a pre-purge period (which will be referred to hereinafter as a pre-purge timer), and this timer 5 starts its timing operation after the reference timer 2 has operated. The pre-purge timer 5 is composed of an AND gate 6 and counters 7, 8 and 9. Reference numeral 10 designates a timer for timing a safety period (which will be referred to hereinafter as a safety timer), and this timer 10 starts its timing operation after the pre-purge timer 5 has operated. The safety timer 10 is composed of an AND gate 11 and counters 12 and 13. The counters in these timers 2, 5 and 10 are inverted by a negative edge.
Reference numeral 15 designates an AND gate, 16 an ignition unit drive terminal, 17 an output circuit, 18 an electromagnetic relay, 19 an ignition unit, and 20 a commercial AC power source. The unit 19 is composed of a resistor 21, a diode 22, a condenser 23, a Sydac 24 and an ignition transformer 25 in a manner well known in the art.
Reference numeral 26 designates a fuel supply unit drive terminal which controls a fuel supply unit via an output circuit and an electromagnetic relay.
Reference numeral 27 designates a terminal in which a temperature signal is applied from a temperature sensing circuit, and the signal is "1" at low temperatures.
Reference numeral 28 designates a memory circuit which operates in response to an abnormality signal and is in the form of an RS flip-flop (which will be referred to hereinafter as RSFF) composed of NAND gates 29 and 30.
Reference numeral 31 designates an alarm signal terminal connected to an external alarm circuit. Reference numeral 32 designates an AND gate, and 33 designates a combustion blower drive terminal which controls a combustion blower via an output circuit and an electromagnetic relay.
Reference numeral 35 designates an input terminal to which an abnormality signal is applied from a circuit which senses an abnormal condition such as an unusual temperature rise or shortage of water in a hot-water boiler, and the signal is "0" in the normal condition. Reference numeral 36 designates an OR gate to which the abnormality signal 35 and a misignition signal are applied, and 38 designates an abnormality signal detecting circuit which comprises a differentiation circuit generating a strobing pulse and a circuit for detecting the strobing pulse and the abnormality signal. This circuit 38 is composed of inverters 39, 40, 41, a capacitance 42 and a NAND gate 43. The clock used for the detection purpose is derived from an AND gate 44.
Reference numeral 45 designates an input terminal to which a flame signal is applied from a flame sensing circuit, and the signal is "0" in the absence of flames. 46 designates a D flip-flop (which will be referred to hereinafter as a DFF) operating as a circuit for detecting the flame signal 45, and this circuit 46 detects the flame signal 45 at a phase different from that of the abnormality signal detecting circuit 38. The DFF 46 is inverted by a positive edge. Reference numeral 47 designates an inverter, and 48 designates an AND gate. Reference numeral 49 designates an inverter.
Reference numeral 51 designates a power transformer, and 52 designates a known reference clock pulse generating circuit which is composed of a resistor 53, a diode 54 and a comparator 55. The phase of the clock pulses used for detecting the abnormality signal is selected to differ from that of the discharge pulses used for ignition.
The operation of the apparatus having such a construction will be described. At first, its general operation will be described, as well as referring to FIG. 2. When now the temperature of the medium to be heated drops and the temperature signal 27 is turned "1" from "0" to the starting operation, output of the NAND gate 29 is turned to "1" to turn the AND gate 32 to "1", and the terminal 33 turns on the blower drive. The combustion blower starts its operation to start pre-purging. At the same time, the individual timers 2, 5 and 10 are released from their reset state, and the reference timer 2 effects its frequency dividing operation on the reference clock pulses 1 generated from the reference clock pulse generating circuit 52. The pre-purge period starts at this time. As Q4 is turned to "1", the pre-purge timer 5 starts its operation. Upon lapse of the pre-purged period, the output Q9 generates "1" to provide an igniting operation starting signal via AND gate 15. The terminal 26 turns on the electromagnetic relay which acts to open the fuel supply unit. At the same time, the output of AND gate 15 is turned to "1", and the terminal 16 turns on the electromagnetic relay 18 which drives the ignition unit 19. Discharge pulses appear from the ignition transformer 25 to start the igniting operation. The operation of the pre-purge timer 5 is stopped by the output Q9.
At the same time, the output Q9 is applied to the AND gate 11 so that the safety timer 10 starts to time the safety period. When ignition is attained by the aforementioned igniting operation and the flame signal "1" is applied from the terminal 45 before the output Q10 is turned into "1", the output of DFF 46 is turned to "1" to turn the output of inverter 47 to "0" and also to turn the output of AND gate 15 to "0". The electromagnetic relay 18 is turned off to stop the operation of the ignition unit 19.
The output of DFF 46 is "0" if the ignition is not attained within the safety period. Upon termination of the safety period, the output of AND gate 48 is turned to "1" to turn the output of OR gate 36 to "1" and to turn the output of the detecting circuit 38 to "0". The memory circuit or RSFF 28 operates as shown by the broken curve in FIG. 2, and the output of NAND gate 29 is now turned to "0" to turn the output AND gate 32 to "0". The timers 2, 5 and 10 are reset, and the individual terminal 16, 26 and 33 are turned to "0" to stop the operation of all the external output units. The alarm signal 31 is turned to "1" to inform the outside of occurrence of an abnormal condition.
The operation is also similarly stopped when the abnormality signal is applied from the terminal 35.
When the temperature signal 27 of "0" instructing stoppage of the operation is applied, the terminals 26 and 33 are turned to "0" to turn off the electromagnetic relays thereby stopping the operation.
The operation of the circuit 38 will next be described with reference to FIG. 3. The waveforms A to R are those appearing at the points A to R respectively in FIG. 1.
The output Q3 of the counter 3 is "0" when the temperature signal 27 is "0". Consequently, the output of AND gate 44 is "0", and the output of NAND gate 43 is "1" regardless of the output of the OR gate 36. Thus, the abnormality signal detecting circuit 38 does not operate during the stoppage of operation of the apparatus.
The counter 3 operates as the temperature signal 27 is turned to "1", that is, when the operation starting instruction is applied. The differentiation circuit in the detecting circuit 38 generates a strobing pulse in response to a positive edge of a clock pulse D appearing at the output of the AND gate 44 so as to permit its detecting operation. The generating timing of this strobing pulse corresponds to the positive edge of the reference clock pulse B.
When no abnormality signal is applied to the terminal 35 or when no misignition signal is applied from the AND gate 48, the output of the OR gate 36 is "0", and the output of the NAND gate 43 continues to be "1".
If an abnormality signal or the misignition signal of "1" is applied from the terminal 35 or from the output of AND gate 48, the OR gate 36 is inverted, and the output of NAND gate 43 is inverted in response to the strobing-pulse generating positive edge of the clock pulse D appearing at the output of the AND gate 44, as shown by the broken curves. The output of RSFF 28 is inverted, and "1" appears now at the output of the NAND gate 30, while "0" appears at the output of the NAND gate 29 so as to stop the operation of the apparatus and to output information of the occurrence of an abnormal condition.
Generation and removal of noise will next be described. Noise is generated at the following times: the turning-on time of the blower, the turning-on time of the ignition unit 19 and fuel supply unit, the turning-off time of the ignition unit 19, the turning-off time of the blower and fuel supply unit, and the generating timing of the discharge pulse from the ignition transformer 25. This noise will now be explained.
When the temperature signal E is turned to "1" to instruct starting of the operation, the terminal 33 is immediately turned to "1" as shown in FIG. 3, and the electromagnetic relay for the blower is turned on to generate a noise N1 at the turning-on time of the blower. No strobing pulse is generated at this time since the output of the counter 3 acting to generate the strobing pulse used for detecting an abnormality signal is "0" at this time. Upon lapse of t2 after the end of the duration t1 of the noise N1, the strobing pulse appears in response to the positive edge of the clock pulse D. Therefore, the influence of this noise N1 can be obviated.
In the next place, a noise N2 is generated at the turning-on time of the ignition unit 19 and fuel supply unit, and at this time, the pre-purge period has just terminated, and "1" has appeared at the output Q9. The appearing timing of this output corresponds to the negative edge of the reference clock pulse B. The influence of this noise N2 can therefore be eliminated.
In the next place, the timing-off time of the ignition unit 19 will be described. When the ignition is attained, and the frame signal J is turned to "1", the output of DFF 46 is inverted to "1" by the inverter 49 in response to the negative edge of the reference clock pulse B, and the output of AND gate 15 is turned to "0" to turn off the electromagnetic relay 18 for the ignition unit 19. This noise N3 is generated in response to the negative edge of the reference clock pulse B, and the influence of this noise can therefore be eliminated.
In the next place, the blower and fuel supply unit are turned off when the temperature signal applied from the terminal 27 is turned to "0". In this case, the counter 3 is reset, and the abnormality signal detecting circuit 38 is not in operation. Therefore, the circuit 38 is not affected by a noise generated due to this off condition.
In the last place, a noise N4 due to a discharge pulse can also be removed since the phase of the discharge pulse generated from the ignition transformer 25 during the igniting operation is also shifted from that of the strobing pulse.
Thus, it is possible to eliminate the influence of noise generation with the on-off operations of the individual electromagnetic relays for the blower, ignition unit 19 and fuel supply unit, the influence of noise generation with the on-off operations of the individual units, and the influence of discharge pulses.
With regard to other noise, its influence can also be eliminated unless it is synchronous.
In the aforementioned embodiment, the detecting clock pulse supplied to the abnormality signal detecting circuit 38 is derived from the AND gate 44 which receives the reference clock pulses 1 and the output of the counter 3 as its inputs. Therefore, the time interval between the time of noise generation and the time of detection can be increased compared with the case in which the output of the counter 3 is used as the detecting clock pulse, while the period of detection is the same. The master slave system provides a large margin against noise when the detecting clock pulse is supplied from the counter 3.
An AND gate may be provided to receive the reference clock pulses 1 and the temperature signal 27 as its inputs, and its output may be applied to the counter 3 and may also be applied as the detecting clock pulse. However, this is undesirable in that a strobing pulse may be generated immediately after the reset condition is released.
In the case of obtaining the detecting clock pulse 1 on the basis of only the reference clock pulse "1" it is impossible to completely prevent noise generation at the on-off time of the blower and at the off-time of the fuel supply unit. Further, the margin against noise is small.
In the aforementioned embodiment, the ignition unit is deenergized by the flame signal 45. However, it may be deenergized in response to, for example, the termination of the safety period timed by the safety timer 10. In this case, there is no influence of noise since the ignition unit is deenergized in response to the negative edge of the reference clock pulse 1. The same applies also to the case in which, when the ignition has been attained, the ignition unit is kept operated for a predetermined period of time by the timer even after the lapse of the safety period.
In the type in which the sequence returns to the pre-purging operation and the re-igniting operation is then carried out in the event of flame extinction in the course of combustion, the influence of the noise generated at the turning-off time of the fuel supply unit can be eliminated since the timer is in the reset state.
Besides the illustrated construction, the abnormality signal detecting circuit 38 may be constructed by the use of a D flip-flop like that used in the flame signal detecting circuit. It can also be obtained by any other construction.
The DFF 46 in the flame signal detecting circuit may be replaced by any other construction.
In the aforementioned embodiment, the timer part is composed of three timers 2, 5 and 10. The arrangement will be similar to that above described even when the timer part is composed of a single timer or more timers.
In the aforementioned embodiment, the timer does not perform its frequency dividing operation when the apparatus is shut down. However, the present invention can be applied to the type of apparatus in which the timer is ready for the frequency division operation, and when the temperature signal is inverted to operation from the shutdown, a pulse is applied for reset and set of the timer so that the timer starts its frequency dividing operation again. However, the abnormality signal detecting circuit 38 is operable in this case. Therefore, unless the RSFF 28 is designed to be reset during shutdown, this RSFF 28 will undesirably be triggered by a noise during the shutdown. The abnormality signal detecting circuit or the memory circuit may be made inoperative for protection from noise during the shutdown operation.
It will be understood from the foregoing description that the present invention comprises a memory circuit which is adapted to operate with timing other than the generation of timing of noise generated from external output units, so that the memory circuit may not be affected by noise.
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|U.S. Classification||431/15, 431/31, 431/77, 431/73, 431/69|
|International Classification||F23N5/20, F23N5/24|
|Cooperative Classification||F23N2031/20, F23N2031/12, F23N5/203, F23N2031/10, F23N5/242, F23N2023/04|
|European Classification||F23N5/20B, F23N5/24B|